The present invention is directed toward a gripping device which utilizes a shape memory alloy as an operative component thereof.
Various types of connectors have been utilized which employ a heat recoverable metallic band made, for example, of Nitinol. Nitinol is an electrically conductive alloy containing large proportions of nickel and titanium. A Nitinol wire, for example, may be stretched up to about 10% of its length and will remain in the stretched state even when the tensile stress used to stretch the wire is removed. If the temperature of the wire is then elevated above its martensitic critical temperature, the wire will return to its original unstretched state as if it had a "memory" of its unstretched length. When the wire contracts to its original length it exerts a contracting force which has been used in various applications. U.S. Pat. No. 4,002,954 discloses the utilization of a Nitinol wire for activating a photographic shutter and sets forth a particular electronic circuit arrangement to provide a current pulse sufficient to heat the Nitinol wire to its critical temperature. U.S. Pat. Nos. 3,740,839 and No. 4,497,527 disclose connecting devices utilizing a socket member with several tines and a band positioned over the tines for biasing them toward their center in a contracted state of the band. The band is made of a heat recoverable metallic material. Additional teachings of heat shrinkage and heat recoverable material may be found in U.S. Pat. Nos. 3,445,898, No. 3,622,941 and No. 4,556,050.
Grippers to date have mostly used either pneumatic or hydraulic actuators to achieve the gripping function. These actuators work fine, but require a fluid such as air or oil. This fluid requirement makes these types of actuators difficult to adapt for use in space applications. Additionally, pneumatic and hydraulic grippers are relatively expensive.
One alternative to the hydraulic/pneumatic gripper, for use in space, are electro-mechanical grippers. These are of basically two types, those that use motors and those that use heat activated bimetallic members to effect closing of the gripper, such as are disclosed in British published application No. 862,174. Both of these methods tend to produce bulky, heavy and cumbersome grippers.
A third alternative is disclosed in U.S. Pat. No. 4,509,517 to Zibelin which discloses a device that closes its jaws upon the shortening of a Nitinol wire. This reference, however, fails to provide a versatile clamping device that can be used for relatively large jaw movements in consideration of the relatively small 8-10% length shrinkage of the Nitinol wire. Further, in the prior art, Zibelin teaching does not provide any mechanism for rapidly and uniformly heating the Nitinol wire. The above-enumerated patents are hereby incorporated by reference.